1. Field of the Invention
This invention generally relates to a bicycle rear derailleur. More specifically, the present invention relates to a bicycle rear derailleur with a chain guide tensioning mechanism.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle rear derailleur.
Typically, bicycle rear derailleurs are designed to change the position of a bicycle chain such that the chain can be positioned to engage any one of a plurality of differing diameter chain sprockets. On many bicycles, a shifter mechanism installed to a bicycle handlebar is manipulated to apply tension to an adjuster cable that extends between the shifter mechanism and the rear derailleur. Changes in the tension on the adjuster cable cause the cable to pull on portions of the rear derailleur. Appropriate portions of the rear derailleur then guide the chain to move accordingly to a different chain sprocket.
Such rear derailleurs typically include a mounting member, a pair of linkage members, a movable member and a chain guide. The mounting member is usually mounted to a portion of a frame of the bicycle. The linkage members are usually connected to the mounting member for pivoting movement with respect thereto. The movable member is usually supported on the linkage member such that the movable member is moveable relative to the mounting member via the pivoting movement of the linkage members. The chain guide is usually supported on the movable member such that the movable member and the chain guide are selectively movable to different positions, corresponding to the locations of the chain sprockets. The chain guide is usually pivotable about a pivot axis that extends through the movable member. A spring member typically biases the chain guide in a direction such that the chain is tensioned by the biasing force of the spring member. The chain is tensioned in order to keep the chain engaged with the chain sprockets.
Spring members used to bias the chain guide usually apply a near linear force to the chain guide. Specifically, the force applied by the spring member increases linearly with angular displacement of the chain guide. Some cyclists have found that as the force on the coil spring increases with angular displacement of the chain guide, friction between the chain and the sprocket also increases which may cause low drive efficiency, rapid wear of sprocket tooth and chain shifting between chain sprockets becomes more difficult.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved chain tensioning arrangement that reduces the force applied to the chain by the chain guide. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.